15,555 research outputs found
The role of attractive forces in viscous liquids
We present evidence from computer simulation that the slowdown of relaxation
of a standard Lennard-Jones glass-forming liquid and that of its reduction to a
model with truncated pair potentials without attractive tails is quantitatively
and qualitatively different in the viscous regime. The pair structure of the
two models is however very similar. This finding, which appears to contradict
the common view that the physics of dense liquids is dominated by the steep
repulsive forces between atoms, is characterized in detail, and its
consequences are explored. Beyond the role of attractive forces themselves, a
key aspect in explaining the differences in the dynamical behavior of the two
models is the truncation of the interaction potentials beyond a cutoff at
typical interatomic distance. This leads us to question the ability of the
jamming scenario to describe the physics of glass-forming liquids and polymers.Comment: 13 pages, 12 figure
Side-Information Coding with Turbo Codes and its Application to Quantum Key Distribution
Turbo coding is a powerful class of forward error correcting codes, which can
achieve performances close to the Shannon limit. The turbo principle can be
applied to the problem of side-information source coding, and we investigate
here its application to the reconciliation problem occurring in a
continuous-variable quantum key distribution protocol.Comment: 3 pages, submitted to ISITA 200
A critical test of the mode-coupling theory of the glass transition
The mode-coupling theory of the glass transition predicts the time evolution
of the intermediate scattering functions in viscous liquids on the sole basis
of the structural information encoded in two-point density correlations. We
provide a critical test of this property and show that the theory fails to
describe the qualitatively distinct dynamical behavior obtained in two model
liquids characterized by very similar pair correlation functions. Because we
use `exact' static information provided by numerical simulations, our results
are a direct proof that some important information about the dynamics of
viscous liquids is not captured by pair correlations, and is thus not described
by the mode-coupling theory, even in the temperature regime where the theory is
usually applied.Comment: 7 pages, 5 figures
Infectious intestinal disease : do we know it all?
Infectious intestinal disease (IID), with associated high morbidity and considerable mortality worldwide, causes a wide spectrum of illness. This ranges from mild discomfort to illness with severe complications. The economic burden from direct and indirect costs may be high. It is acquired by oral ingestion of micro-organisms which are transmitted from person to person; via food or water or through contact with animals or contaminated objects. Viruses are the commonest cause in developed countries. In Malta, medical practitioners and laboratories are the main source of data on IID. However, under-reporting is a problem. In order to fill in the lacunae in information on the disease burden, population-based-studies are required. Along with other countries, Malta has embarked on a number of studies to describe and quantify under-reporting of IID. This may assist in strengthening the surveillance system which, in combination with other measures, should result in an improvement of the control of IID.peer-reviewe
First-principles calculations of the crystal structure, electronic structure, and thermodynamic stability of Be(BH4)2
Alanates and boranates are intensively studied because of their potential use as hydrogen storage materials. In this paper, we present a first-principles study of the electronic structure and the energetics of beryllium boranate BeBH42. From total energy calculations, we show thatâin contrast to the other boranates and alanatesâhydrogen desorption directly to the elements is likely and is at least competitive with desorption to the elemental hydride BeH2. The formation enthalpy of BeBH42 is only â0.14 eV/H2 at T=0 K. This low value can be rationalized by the participation of all atoms in the covalent bonding, which is in contrast to the ionic bonding observed in other boranates. From calculations of thermodynamic properties at finite temperature, we estimate a decomposition temperature of 162 K at a pressure of 1 bar
Laboratory surveillance of communicable diseases : enteric pathogens
Laboratories represent a crucial link in the surveillance chain. Since only a small proportion of cases of enteric infections are asked to submit a stool sample, one needs to assess the practices for testing for enteric pathogens and their notification practices. Five local laboratories participated in this study. This included a description of the laboratory practices; capacity for stool sample analysis; awareness of the notification system and the factors which could improve the system at laboratory level.peer-reviewe
Chaining of welding and finish turning simulations for austenitic stainless steel components
The chaining of manufacturing processes is a major issue for industrials who want to understand and control the quality of their products in order to ensure their in-service integrity (surface integrity, residual stresses, microstructure, metallurgical changes, distortions,âŠ). Historically, welding and machining are among the most studied processes and dedicated approaches of simulation have been developed to provide reliable and relevant results in an industrial context with safety requirements. As the simulation of these two processes seems to be at an operationnal level, the virtual chaining of both must now be applied with a lifetime prediction prospect. This paper will first present a robust method to simulate multipass welding processes that has been validated through an international round robin. Then the dedicated âhybrid methodâ, specifically set up to simulate finish turning, will be subsequently applied to the welding simulation so as to reproduce the final state of the pipe manufacturing and its interaction with previous operations. Final residual stress fields will be presented and compared to intermediary results obtained after welding. The influence of each step on the final results will be highlighted regarding surface integrity and finally ongoing validation works and numerical modeling enhancements will be discussed
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